Custom Discount not apply after customer login

Question

I created the discount programatically by sales_quote_collect_totals_after event.

This discount applies only when cart subtotal greater than 500. This discount works good in cart page. After customer login, this discount is removed automatically.I tried this Refer link, but not working.The below which I used in sales_quote_collect_totals_after event

 $discountAmount = 0;
        $quote = $observer->getQuote();

    $quoteitems = $quote->getAllItems();
    foreach ($quoteitems as $item) {
        /*@var $quoteItem Mage_Sales_Model_Quote_Item */
        $product = $item->getProduct();
        $totalprice += $quote->getBaseSubtotal();
        //exit;

    }

    if($$totalprice>500) {
    $discount = 100;
        $total=$quote->getBaseSubtotal();
        $quote->setSubtotal(0);
        $quote->setBaseSubtotal(0);

        $quote->setSubtotalWithDiscount(0);
        $quote->setBaseSubtotalWithDiscount(0);

        $quote->setGrandTotal(0);
        $quote->setBaseGrandTotal(0);

        $canAddItems = $quote->isVirtual()? ('billing') : ('shipping'); 
        foreach ($quote->getAllAddresses() as $address) {

            $address->setSubtotal(0);
                $address->setBaseSubtotal(0);

                $address->setGrandTotal(0);
                $address->setBaseGrandTotal(0);

                $address->collectTotals();

                $quote->setSubtotal((float) $quote->getSubtotal() + $address->getSubtotal());
                $quote->setBaseSubtotal((float) $quote->getBaseSubtotal() + $address->getBaseSubtotal());

                $quote->setSubtotalWithDiscount(
                    (float) $quote->getSubtotalWithDiscount() + $address->getSubtotalWithDiscount()
                );
                $quote->setBaseSubtotalWithDiscount(
                    (float) $quote->getBaseSubtotalWithDiscount() + $address->getBaseSubtotalWithDiscount()
                );

                $quote->setGrandTotal((float) $quote->getGrandTotal() + $address->getGrandTotal());
                $quote->setBaseGrandTotal((float) $quote->getBaseGrandTotal() + $address->getBaseGrandTotal());

            $quote ->save(); 

            $quote->setGrandTotal($quote->getBaseSubtotal()-$discountAmount)
            ->setBaseGrandTotal($quote->getBaseSubtotal()-$discountAmount)
            ->setSubtotalWithDiscount($quote->getBaseSubtotal()-$discountAmount)
            ->setBaseSubtotalWithDiscount($quote->getBaseSubtotal()-$discountAmount)
            ->save(); 

            if($address->getAddressType()==$canAddItems) {

                    $address->setSubtotalWithDiscount((float) $address->getSubtotalWithDiscount()-$discountAmount);
                    $address->setGrandTotal((float) $address->getGrandTotal()-$discountAmount);
                    $address->setBaseSubtotalWithDiscount((float) $address->getBaseSubtotalWithDiscount()-$discountAmount);
                    $address->setBaseGrandTotal((float) $address->getBaseGrandTotal()-$discountAmount);
                if($address->getDiscountDescription() || $address->getDiscountAmount()){
                    $address->setDiscountAmount(-($address->getDiscountAmount()-$discountAmount));
                    $address->setDiscountDescription($address->getDiscountDescription().', Free Samples');
                    $address->setBaseDiscountAmount(-($address->getBaseDiscountAmount()-$discountAmount));
                }
                else {
                    $address->setDiscountAmount(-($discountAmount));
                    $address->setDiscountDescription('Free Samples');
                    $address->setBaseDiscountAmount(-($discountAmount));
                }
                $address->save();
            }
        }
    }

Answer 1

In config.xml , use load_customer_quote_before event

<load_customer_quote_before>
    <observers>
        <custom_checkout_observer>
            <type>singleton</type>
            <class>yourNamespace_yourModule_Model_Observer</class>
            <method>loadCustomerQuote</method>
        </custom_checkout_observer>
    </observers>
</load_customer_quote_before>

In observer.php

  <?php
    class YourNamespace_YourModule_Model_Observer extends Mage_Checkout_Model_Session {

        public function loadCustomerQuote() {

            $quote =Mage::getSingleton('checkout/session')->getQuote();
            $quote->getBillingAddress();
            $quote->getShippingAddress();
            $quote->setCustomer(Mage::getSingleton('customer/session')->getCustomer())
                    ->setTotalsCollectedFlag(false)
                    ->collectTotals()
                    ->save();
            return $this;

        }
}

the above code will set the customer to quote before merge.Now the custom discount works good after merge quote.